Highly recoverable pyridinium-tagged Hoveyda–Grubbs pre-catalyst for olefin metathesis. Design of the boomerang ligand toward the optimal compromise between activity and reusability

Whereas the boomerang ligand of Hoveyda-Grubbs pre-catalysts can be modified by attachment of a pyridinium tag to its benzylidene moiety, a precise adjustment of the length of the spacer allows the optimum balance to be reached between the activity of the catalyst and its recoverability, exceeding 98% after 6 catalytic runs in the best case.